In various commercial and military systems there is a need to estimate the position of the system on the surface of the Earth. Related art Global Positioning System (GPS) receivers, or other similar instruments receiving signals from other constellations of satellites, may provide such position information, but GPS receivers may suffer from purposeful, accidental, and/or natural interference which may degrade and/or deny the performance of the system.
This may be especially critical in military use, where GPS denial can lead to tactical disadvantages. GPS-type approaches may also suffer from a large power draw associated with receiving the weak GPS signals, reducing battery life of portable receiver units and leading to long times required to lock on to the system's location, especially if there is no initial guess of the system's position.
To reduce the impact of GPS denied/degraded systems, inertial measurement units (IMUs) comprising 3-axis accelerometers and 3-axis gyroscopes may be used to measure the acceleration and rotation rates of the system and integrate these to provide an estimate of the position and orientation relative to a known starting point. However, the accuracy of this type of navigation (known as “dead-reckoning”) may degrade with time because of drift of the sensors arising due to their noise.
Thus, there is a need for a position-estimating system providing stable accuracy and that does not rely on information received from a constellation of satellites.